Check if a variable contains a numerical value in Javascript?

Question

In PHP, it's pretty easy:

is_numeric(23);//true
is_numeric("23");//true
is_numeric(23.5);//true
is_numeric(true);//false

But how do I do this in Javascript? I could use a regular expression, but is there a function for this?

Answer 1

What about:

function isNumber(n){
    return typeof(n) != "boolean" && !isNaN(n);
}

The isNaN built-in function is used to check if a value is not a number.

Update: Christoph is right, in JavaScript Boolean types are convertible to Number, returning the 1 for true and 0 for false, so if you evaluate 1 + true the result will be 2.

Considering this behavior I've updated the function to prevent converting boolean values to its numeric representation.